1. Field of the Invention
The present invention relates to a technique of creating ink dots of respective colors on a printing medium, so as to print a high-quality color image.
2. Description of the Related Art
Diverse imaging apparatuses that deal with color images, such as digital cameras, color scanners, color monitors, and color printers, have been used widely. Any of such imaging apparatuses treats each color image as a composition of three image components, R, G, and B image components corresponding to three primary colors of light. The shooting apparatuses like digital cameras and color scanners output RGB tone levels corresponding to the R, G, and B images as color image data. Based on the output RGB tone levels, for example, the color monitor forms the respective R, G, and B images and combines these three images on the screen to display a color image. The color printer converts the RGB tone levels of the input image data into tone levels of cyan (C), magenta (M), and yellow (Y) processible in the printer and makes dyes of cyan, magenta, and yellow applied on the printing medium by any of various techniques according to the converted CMY tone levels, so as to print a color image.
RGB image data output from the shooting apparatuses like digital cameras and color scanners may depend upon the model of the shooting apparatus. This is because different models have different sensitivities of a detector that separates the color image into three color components corresponding to three primary colors of light, that is, the R image component, the G image component, and the B image component. The color expressed on the monitor or the printing medium in response to input of identical RGB image data may be varied subtly according to the type of the color monitor or the color printer. In the case of the color monitor, different models may have subtly different sensitivities of the respective R, G, and B images displayed on the screen based on the RGB image data. In the case of the color printer, different models may have subtle differences in development of the respective colors, cyan, magenta, and yellow. In order to attain expression of the original colors with the color monitor or the color printer, it is required to make the characteristics of the output side of the RGB image data like the digital camera and the color scanner coincident with the characteristics of the input side of the RGB image data like the color monitor and the color printer.
It is undesirably time- and labor-consuming to adjust the characteristics of the output side of RGB image data and the characteristics of the input side of RGB image data every when the combination of these imaging apparatuses is changed. The following technique has thus been adopted widely. The technique assumes a virtual reference detector having a predetermined sensitivity and specifies RGB image data output from this virtual detector as standard r. sRGB image data is typically used as the standard image data. The shooting apparatuses like digital cameras and color scanners convert the RGB image data into the standard image data (sRGB image data) and output the converted standard image data. The characteristics of the color monitor and the color printer are adjusted to enable accurate reproduction of colors of the standard RGB image data (sRGB image data). This procedure ensures accurate reproduction of original colors, irrespective of the characteristics of the shooting apparatus that outputs image data and irrespective of the characteristics of the apparatus that receives the processed image data.
The prior art method, however, does not ensure the satisfactory picture quality even when the color printer accurately reproduces the standard RGB image data. The recent advancement has improved the printing quality of the color printer and enables images of high picture quality comparable to the quality of silver halide photographs to be printed. The vividness of the images printed with the color printer is, however, not so high as that of the silver halide photographs. This leads to unsatisfactory picture quality of the printed images.